This invention relates to the construction of improved liquid crystal displays. The invention pertains to the manner in which the liquid crystal display (LCD) panel is electrically connected to the electronic driver assemblies which provide electrical control for the thin film transistor (TFT) matrix on the liquid crystal panel. More specifically this invention presents a compact, rugged approach to the assembly of the liquid crystal display module.
Generally, liquid crystal displays are an assembly comprising a glass panel unit (which is a thin film transistor matrix controlling a liquid crystal emulsion contained between transparent glass plate electrodes), driver electronics which provide the control signals to the TFT matrix, and a lighting unit placed beneath the glass panel unit for illuminating the LCD panel. The glass panel unit is comprised of a transparent glass substrate upon which the TFT matrix is placed (the LCD or panel substrate), a second conducting transparent glass plate placed a small distance from and parallel to the panel substrate, filled in-between with the liquid crystal material, and sealed around the edges. The entire assembly is housed by a frame, and usually has the driver assemblies attached to the frame near the front surface of the panel substrate which contains the TFT array.
The driver assemblies consist of a circuit board mounted on, or integral with, a "flex" print. The driver components are usually in the form of packaged chips either surfaced mounted or wire bonded to the circuit board. A heat sink is mounted on the reverse side of the "flex" behind the circuit board. The use of flex print circuits is generally subject to numerous electrical faults, but does give the benefit of providing flexibility of the electrical connections which can act to protect against vibration and other mechanical stresses which occur from the nature of this configuration.
The electrical output connection from the flex print to the TFT electrical contacts located on the front surface of the panel substrate is usually made with epoxy bonds. However, alternate interconnection can be made by wire bonding between the "flex" print and the panel substrate conductors. Both of these methods usually allow up to 80 connections per inch. The size of additional peripheral space required on existing LCD substrate panels beyond the active TFT area can be greater than one inch. This has the effect of making the LCD much larger than the viewable area.
The article "A Ten Inch Diagonal High Resolution Active Matrix Color LCD Module" by Kenichi Niki et al published in the 1988 Proceedings of the SID, pp. 259-263, shows the method of electrically connecting the driver integrated chip assemblies using flexible printed circuit straps. Their FIGS. 6 and 7 illustrate the technique that has generally been used in the prior art.